Studies are undertaken in four general categories. a) Studies concerning aortocoronary vein bypass grafting are designed to help determine factors that favor graft patency, the preference of internal mammary or saphenous vein and the factors in the perioperative period that are responsible for myocardial infarction. Studies include assessment of drugs that might limit the amount of muscle loss in myocardial infarction during operative treatment of coronary occlusive disease. b) Studies are conducted to determine the ability of transplanted organs to grow; the correlation of functional rejection with histology and biochemistry; and methods of preserving donor organs for transplantation. Preservation techniques being studied are freezing and perfusion. The effect of immunosuppressive regimens on atherosclerosis is being studied. c) The studies on cardiac innervation effects on coronary flow are undertaken to attempt to determine if alteration of the autonomic inflow and/or outflow from the heart would be favorable to the patient with coronary obstructive disease. The studies evaluate the effect of the autonomic nervous system on rhythm as well as coronary flow and distribution. d) Substitution for the heart by mechanical means involves assessment of an artificial left ventricle pumping from the ventricle to the aorta. The potential for myocardial injury to reverse in the presence of work reduction by mechanical support is also investigated.